Chemical mechanical polishing (CMP) process is widely used for planarization during fabrication of semiconductor devices. In general, CMP process involves polishing a surface of a semiconductor wafer on a polishing surface, e.g., a polishing pad, using a solution, e.g., a slurry solution, supplied between the wafer surface and the polishing surface. Depending on the CMP process, multiple CMP steps may be performed to produce a single planarized layer on the semiconductor wafer. As an example, multiple CMP steps may be performed during fabrication of a semiconductor device with copper damascene structures.
In order to facilitate multi-step CMP processes, CMP equipments with multiple polishing stations have been developed. A concern with conventional CMP equipments is that each CMP equipment can only perform specific multi-step CMP processes, which depends on the number of polishing stations of that CMP equipment. For example, a CMP equipment with two serially arranged polishing stations, which is designed for two-step serial CMP processes, cannot perform three-step serial CMP processes.
In view of this concern, what is needed is a polishing apparatus that can perform different multi-step CMP processes.